1. Field of the Disclosure
This invention relates to surgery, and more particularly, to air barriers used to reduce contamination of surgical sites.
2. Background Art
Hospital-acquired infections (“HAI”), also known as nosocomial infections, are a significant problem in modern healthcare systems. In 2002, approximately 1.8 million people contracted an HAI in U.S. healthcare facilities, and approximately 100,000 died as a result. HAI dramatically increases patient length of stay and cost and decreases hospital bed availability for other patients. The second most prolific cause of HAI is surgical site infections (“SSI”), which account for about 22% of all nosocomial infections. Hollenbeak C S, et al., The clinical and economic impact of deep chest surgical site infections following coronary artery bypass graft surgery, CHEST, 118 (2) (August 2000); National Nosocomial Infections Surveillance (NNIS) System Report, data summary from January 1992 through June 2004, issued October 2004, Centers for Disease Control and Prevention, publ. AMERICAN JOURNAL OF INFECTION CONTROL, 32, 470-85 (2004); Chu VH, et al, Staphylococcus aureus bacteremia in patients with prosthetic devices: costs and outcomes, THE AMERICAN JOURNAL OF MEDICINE, 118 (12) (December 2005); Klevens N R, et al., Healthcare-associated infections and deaths in U.S. hospitals, 2002, PUBLIC HEALTH REPORTS, 122, 160-166 (March-April 2007).
SSI infections mostly are “staph” infections, caused by the bacterium Staphylococcus aureus, which occurs harmlessly on human skin and frequently in the nose. If these bacteria gain access to a normally sterile space, such as in the capsule of a joint, they may multiply without resistance and create a huge infectious burden on the host. They often attach to prosthesis surfaces and multiply within dense aggregations called biofilms. Bacteria protected within biofilms are much harder to kill than individual isolated bacteria. SSI from bacterial invasion is particularly deleterious in procedures such as orthopedic joint arthroplasty, cardiovascular surgery, and neurosurgery. These types of infections develop deep within the body, are difficult to treat, and are devastating to patients. Antibiotics can't always penetrate tissues to reach bacteria that have taken root on implanted materials, and revision surgery on the infected joint is often necessary to eradicate the infection. Sometimes the infection will have caused so much bone loss that a second prosthesis replacement isn't an option, in which case the only option is fusing the bones together leaving the joint stiff and immobile and the patient in need of a mobility aid.
Airborne bacteria present in the operating room environment are a leading cause of SSI. A primary vector of microbial intrusion into the surgery site is direct precipitation from the atmosphere. Bacteria are generally 0.5-1 μm in size or larger and have a tendency to cluster together and attach to other larger particles. Airborne bacteria-carrying particles measure about 4 μm to 20 μm. Humans constantly shed skin scales in the 5-20 μm particle range into the atmosphere. Most current research regarding the vectors of airborne bacteria into the surgery site is based upon a study performed in 1982, Whyte W. et al., The importance of airborne bacterial contamination of wounds, JOURNAL OF HOSPITAL INFECTION, Vol. 3(2), 123-135 (June 1982). Whyte estimated that the source of about 98% of the bacteria present in a surgical wound was airborne. Studies indicate that controlling the presence of bacteria in the operating room atmosphere can reduce the risk of SSI.
Laminar flow operating rooms (“LFOR”) were developed in the 1970's and 1980's to reduce the incidence of SSI from airborne bacteria. In a LFOR, clean air is introduced from filters in either the ceiling (vertical flow) or side wall (horizontal flow) at low speeds, e.g., 20 to 40 m/min (66 to 132 ft/min), to preserve laminar flow. The benefit thought to be achieved by LFOR air distribution is that filtered air flowing in laminar streams does not mix with contaminated air before reaching the surgery site, thus preventing airborne bacteria from reaching the surgery site. However, the ability of LFORs to accomplish this and prevent infections is qualified and debatable. Ritter M A, et al., The operating room environment as affected by people and the surgical face mask, CLINICAL ORTHOPEDICS, 111, 147-150 (September 1975); Franco J A, et al., Airborne Contamination in Orthopedic Surgery. Evaluation of Laminar Air Flow System and Aspiration Suit, CLINICAL ORTHOPAEDICS AND RELATED RESEARCH, Number 122 (January-February, 1977); Ritter M A, et al., Comparison of Horizontal and Vertical Unidirectional (Laminar) Air-flow Systems in Orthopedic Surgery, CLINICAL ORTHOPAEDICS, 129 (November-December 1977); Ritter M A, et al., Laminar Air-Flow Versus Conventional Air Operating Systems: A Seven-Year Patient Follow-Up, CLINICAL ORTHOPAEDICS, 150 (July-August 1980); Whyte W, et al., The importance of airborne bacterial contamination of wounds, Journal of Hospital Infection, 3(2), 123-135 (June 1982); Lidwell O M, et al., Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study, British Medical Journal, Vol. 285 (July 1982); Lidwell O M, et al., Airborne contamination of wounds in joint replacement operations: the relationship to sepsis rates, JOURNAL OF HOSPITAL INFECTION, 4 (2), 111-131 (June 1983); Horworth F H, Prevention of Airborne Infection during Surgery, ASHRAE TRANSACTIONS, 91(1b), 291-304 (1985); Horworth F H, Prevention of Airborne Infections in Operating Rooms, HOSPITAL ENGINEERING, 40 (8), 7-23 (1986); Charnley, J, A clean-air operating enclosure, THE CLASSIC, Number 211 (October 1986); Lidwell O M, et al., Ultraclean air and antibiotics for prevention of postoperative infection. A multicenter study of 8,052 joint replacement operations, ACTA ORTHOPAEDICA SCANDINAVICA, 58, 4-13 (1987); Van Griethuysen A J A, Surveillance of wound infections and a new theatre: unexpected lack of improvement, JOURNAL OF HOSPITAL INFECTION 34, 99-106 (1996); Ritter M A, Operating room environment, CLINICAL ORTHOPAEDICS & RELATED RESEARCH, 369, 103-109 (December 1999); Persson M, et al., Wound ventilation with ultraclean air for prevention of direct airborne contamination during surgery, INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, 25 (4) (April 2004); Clarke M T, et al., Contamination of primary total hip replacements in standard and ultra-clean operating theaters detected by the polymerase chain reaction, ACTA ORTHOPAEDICA 75 (5), 544-548 (2004); Pereira M L, et al., A Review of Air Distribution Patterns in Surgery Rooms under Infection Control Focus, ENGENHARIA THERMICA (Thermal Engineering), 4 (2), 113-121 (October 2005); Miner A L, et al., Deep Infection After Total Knee Replacement: Impact of Laminar Airflow Systems and Body Exhaust Suits in the Modern Operating Room, INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, 28 (2), (February 2007); Pasquarella C, et al., A mobile laminar airflow unit to reduce air bacterial contamination at surgical area in a conventionally ventilated operating theatre, JOURNAL OF HOSPITAL INFECTION, 66 (4), 313-319 (August 2007).
While laminar flow air is clean when leaving the air vents in the wall or ceiling, it must traverse a significant distance in a room laden with contaminants and will entrain ambient particles in its flow. Overhead lights and staff leaning over the patient are regularly interposed between the clean air source and the surgery site, creating a direct vector for contaminants to compromise the patient. Recent studies have shown that the primary source of the airborne contamination in the operating room, assuming HVAC systems are properly designed and maintained, is the shedding of bacteria and particulate matter, such as skin scales bearing bacteria, by people present in the operating room, including personnel outside the sterile surgical field (circulating nurses, anesthesiologists, radiology technicians and other technicians). See e.g., Edmiston Jr. C E, et. al., Molecular epidemiology of microbial contamination in the operating room environment: Is there a risk for infection?SURGERY, 138:573-582 (October 2005). In other words, the inclusion of surgical personnel and equipment within the air barrier may limit the ability of LFOR systems to reduce airborne microbes arising from those people and that equipment. Moreover, laminar flow operating theatres are uncommon and costly. Installing one laminar flow surgery room costs at least about $500,000, is a major construction project, and disrupts surgery room availability.
An alternative approach to LFOR systems has been to move a source of sterile air closer to the patient or the operating table. U.S. Pat. 3,820,536 (Anspach Jr. et al., 1974) describe bringing a high efficiency particulate air filter (“HEPA”) blower up to an operating table and angling the blown air downwardly onto the patient. In a study, Thore M, et al., Further bacteriological evaluation of the TOUL mobile system delivering ultra-clean air over surgical patients and instruments, JOURNAL OF HOSPITAL INFECTION 63, 185-192 (2006), a freestanding mobile laminar flow clean air source was evaluated, similar to the device described in U.S. Pat. No. 3,820,536. The device was positioned approximately 2 m away from the surgery site at an elevation above and angled down toward the site and said to have delivered laminar flow HEPA air toward the surgical field. Since the device could be positioned closer to the surgery area than would be the case where the air source is built into the infrastructure of the room, it was thought that the contamination effect of room traffic would be reduced. During actual surgery, Thore et al. found that the device was ineffective after the air traveled further than approximately 1 m from the unit due to the room dynamics between the air source and the surgery site.
Others that have tried moving the source of sterile air closer to the patient or the operating table include Meyer as described in U.S. Pat. No. 4,275,719 (1981) and Smets as described in U.S. Pat. No. 4,422,369 (1983). Mayer described a pair of nozzles flat in cross section aligned on either side of an incision area (one nozzle to blow sterile air, the other to collect it) with the nozzles held in place with strips of tape. Smets described a system in which a curtain of sterile air is formed above a surgical table also using aligned blower and suction nozzles. A drape reaches from the lower edge of the blower nozzle to the surface of a table to prevent entrainment of ambient air beneath the blower nozzle. This arrangement set up a turbulent circulation under the blower nozzle. A nozzle in the shape of a flattened cone is placed on the surface of the table to flow sterile air into the circulation opposite the direction of flow of the overhead air curtain to neutralize disturbances caused by the gas curtain.
Other than LFOR's, the only solution finding its way into mainstream utilization has been body exhaust suits (“BES”), also developed in the 70's and 80's. Colloquially called a “space suit,” these consist of a plastic helmet with a built-in filter over which a sterile hood with a view pane is placed to completely encapsulate the surgeon's face and neck. Contaminants from the surgeon's head region are captured and filtered before the air is exhausted back into the operating room. The ability of BES to prevent contamination of the surgery site is viewed as unproven. Franco J A, et al., CLINICAL ORTHOPAEDICS AND RELATED RESEARCH (1977), ibid; Der Tavitian J, et al., Body-exhaust suit versus occlusive clothing—a randomized, prospective trial using air and wound bacterial counts, JOURNAL OF BONE AND JOINT SURGERY (British), 85-B:4, 490-494 (2003); Miner A L, et al., INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, ibid; Ritter M A, CLINICAL ORTHOPAEDICS & RELATED RESEARCH (2007), ibid. Body exhaust suits isolate the surgeon, not the patient. Moreover, typically, only surgical personnel working in the operating room within the surgical field (surgeons, surgical assistants and technicians, and scrub nurses) wear the suits during a surgery.
Beyond the mainstream LFOR and BES solutions, virtually no new technology has emerged and been generally adopted over the past 30-plus years to remove the source or cause of SSI, and even the LFOR and BES approaches to the SSI problem are rarely used outside of orthopedic joint replacement surgery because they are so costly and complicated. As a result, the incidence of SSI remains largely unabated. Innovations currently being pursued in research and industry to combat SSI infection have shifted primarily from preventive solutions for the operating room to post operative pharmaceutical solutions, directed to creating antibacterial drugs that would prevent infections from developing post-operatively and would mitigate the effects of infection once microorganisms enter the body. History is testament that drug resistant bacteria develop as a result of application of antibacterial drugs.
The root problem remains: how to prevent bacteria shed by personnel in the operating room from invading the surgical wound during surgery. A second part is how to solve the root problem in a way that can facilitate widespread adoption of the solution and by widespread adoption significantly combat and reduce SSI. For widespread adoption, the solution must not only be effective, it has to be cost effective, and it should be easy for surgeons and staff to implement. Yet, for more than 30 years since initial appreciation of the root cause of SSI, and despite urgent need and serious efforts of many dedicated professionals, scientists and engineers to address the root problem, SSI from operating room bacteria remains a serious unresolved health care issue.
The present invention is directed to the root cause of the SSI problem: effectively preventing bacterial invasion of a surgically created wound during the surgery; and is also directed to the second part of the problem: making the solution effective, inexpensive and easy to implement. The invention has particular advantage for surgical procedures involving deep, “clean” anatomical structure, for example, without limitation, orthopedic joint arthroplasty, pediatric ventricular shunt implantation, cardiac implant and vascular surgery, and long-duration procedures.